Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$123.39	13.130%	$139.5911	$139.59	$139.60	$139.60
Purchase #2	$209.92	3.438%	$217.137	$217.14	$217.15	$217.10
Purchase #3	$95.49	8.671%	$103.7699	$103.77	$103.75	$103.80
Purchase #4	$49.51	3.787%	$51.3849	$51.38	$51.40	$51.40
Purchase #5	$79.44	12.789%	$89.5996	$89.60	$89.60	$89.60
Purchase #6	$142.43	3.699%	$147.6985	$147.70	$147.70	$147.70
Purchase #7	$185.79	4.677%	$194.4794	$194.48	$194.50	$194.50
7 purchase totals =	$885.97		$943.6604	$943.66	$943.70	$943.70